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I have one enphase microinvertor for each panel. They feed AC to the main panel. I suspect the inverter in the powerwall, is converting DC from the powerwall battery to the AC used around the house. That would put the investor after the battery. I'm don't see how the AC from the enphase micros can charge the powerwall battery unless another invertor is used. I hope I'm wrong on this. Right after I post, I'm googling battery storage on microinverter ststems to see if there's a trick.

I'm don't see how the AC from the enphase micros can charge the powerwall battery unless another invertor is used

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Here is how I do it with Enphase Inverters. My system is inefficient but it enables me to load shift and maximize the energy I sell to the utility. The Enphase Inverters to their thing during the day. During peak hours I used grid use timers on my outback inverter to run my critical loads off the batteries, which maximizes the energy from the Enphase inverter that gets sold. At night I use a separate lithium battery charger on a timer to charge my pack at cheap rates. It would be less expensive if everything was integrated but it works for me, has a small return and gives me the security of a backup. Long term if California ever gets to a network of demand response and distributed energy resources I might make a little more money feeding energy to the grid at critical time. That would mean I would have to have an intertie agreement for my Outback inverter. Currently it does not sell energy from the battery to the grid.

There are Powerwall 2 specs out there which list both AC inverter and DC inverter round-trip efficiencies (with DC inverter efficiencies being a few points higher) which indicate that the Powerwall 2 will function as a standalone unit capable of charging from the grid.

This also means that the Powerwall 2 will integrate with any solar PV system since the AC Powerwall 2 does not even need to know that the system exists.

So those the powerwall 2.0 with microinverters? can I go off the grid?

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Yes, the Powerwall 2 will control a fancy switch that cuts off grid power when it doesn't detect current. It will then turn on it's inverter and energize the house. Your micro inverters will detect that power is back online and start doing their thing. If there's a surplus of power, the battery will charge from the AC your solar sends out. If there's a deficiency, the house is pulling a heavy load, clouds are blocking the panels, etc., it will turn up the inverter output.

Could I charge the Tesla battery with an external generator -- say ... my car ?
If so, I'll have to give serious thought to cutting my connection to the grid since they are making it expensive to put up PV due to bureaucratic demands and my connection fee is over $30 a month.

Could I charge the Tesla battery with an external generator -- say ... my car ?
If so, I'll have to give serious thought to cutting my connection to the grid since they are making it expensive to put up PV due to bureaucratic demands and my connection fee is over $30 a month.

Thanks, but I don't understand electricity well enough to answer my question from the website. I gather that the 'Prius Plug-out' is a DC to120V AC inverter meant to supply home loads in an emergency.

My question is whether 12v DC current from the accessory battery of the Prius can be used to fill up the Tesla battery in cases of multiple days of no sun and therefore no PV. This situation does not happen often in my sunny locale of SW Colorado, and our home pretty consistently uses about 5-6 kWh a day of electricity, so a one kW output from the Prius to my proposed off-grid island would be enough to run the house and top off the Tesla battery when needed.

Is it possible ?
What would be required beyond a Tesla battery and a DC PV array ?

Thanks, but I don't understand electricity well enough to answer my question from the website. I gather that the 'Prius Plug-out' is a DC to120V AC inverter meant to supply home loads in an emergency.

My question is whether 12v DC current from the accessory battery of the Prius can be used to fill up the Tesla battery in cases of multiple days of no sun and therefore no PV. This situation does not happen often in my sunny locale of SW Colorado, and our home pretty consistently uses about 5-6 kWh a day of electricity, so a one kW output from the Prius to my proposed off-grid island would be enough to run the house and top off the Tesla battery when needed.

Is it possible ?
What would be required beyond a Tesla battery and a DC PV array ?

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The site that shows the Prius Plug-Out solutions has a range of products. The more interesting ones are the high power solutions. They provide a way to get energy out of the high voltage hybrid pack using a datacenter UPS inverter that is designed for battery packs in the same voltage range. Those provide 3kVA or 5kVA with split phase 120/240 VAC output. When you leave the Prius "ON", it will automatically start the engine to recharge the hybrid battery and then shut down again. I would not consider a solution that is based on 12 VDC.

You didn't present a clear enough off-grid scenario for us to judge the suitability.

You didn't present a clear enough off-grid scenario for us to judge the suitability.

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Please ask for any details you need not yet provided.

I would not consider a solution that is based on 12 VDC.

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Why ?
If I understand the alternatives, they are based on a permanent connection to the traction battery. Beyond not needing more than a 1 kW supply, I'm not keen to mess with the traction battery.

I called Tesla this morning and was told that an off-grid use case is possible. I then asked if the battery could take generator input and was told yes, but the CSR would look into more details and send them to me later. He also mentioned that some states (e.g Texas) do not allow off-grid systems. This seems quite odd but I did not ask for further details.The CSR tried to gently steer me towards a grid-tie install since he presumed my consumption pattern would be ~ American average. Since it is not I am going to stay interested in the option unless I find out that technical barriers are still too great for me to overcome at my low level of technical expertise and modest budget.

Why ?
If I understand the alternatives, they are based on a permanent connection to the traction battery. Beyond not needing more than a 1 kW supply, I'm not keen to mess with the traction battery.

I called Tesla this morning and was told that an off-grid use case is possible. I then asked if the battery could take generator input and was told yes, but the CSR would look into more details and send them to me later. He also mentioned that some states (e.g Texas) do not allow off-grid systems. This seems quite odd but I did not ask for further details.The CSR tried to gently steer me towards a grid-tie install since he presumed my consumption pattern would be ~ American average. Since it is not I am going to stay interested in the option unless I find out that technical barriers are still too great for me to overcome at my low level of technical expertise and modest budget.

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I assume we're talking about using a Prius as a backup generator. You can certainly get 1,000 Watts out of a 12V inverter, but you would have to get a very good one to survive years of repeated multi-hour full load usage. The drawback is that you will have additional conversion losses and the Prius has a very small 12V battery. You will have to find the ideal connection point to tap the 12V system to take out the 100 amps you will need. My understanding is that the Prius does not have a 12V alternator and only powers the 12V system with a DC/DC converter from the hybrid battery pack. So, the generation is efficient, but the conversion to 12V has some losses on top of the inverter efficiency. You would also have to confirm the rating of the DC/DC converter to see if it can sustain extended periods of 100 amp output, or you would have to monitor the 12V voltage continuously for an extended period while running the 12V inverter at your intended operating point.

Details - start with the big picture. This thread is about PowerWall 2.0 + Enphase. You are asking about off-grid.
- Do you want to take your Enphase solar off-grid?
- Will you add new solar directly connected to the PowerWall inter-operating with the existing Enphase solar?
- How many watts of solar for each?
- At your location, what is your min and max generation across seasons for your existing solar?
- What is your peak draw from household loads?
- How many PowerWall units do you think you need?
- What is your kWh usage across seasons?
- Have you modeled your energy shortfall in the Winter? This would include looking through your history for consecutive low generation days.
- How did you reach the conclusion that you only need 1kW backup supply?

Yes, the Powerwall 2 will control a fancy switch that cuts off grid power when it doesn't detect current. It will then turn on it's inverter and energize the house. Your micro inverters will detect that power is back online and start doing their thing. If there's a surplus of power, the battery will charge from the AC your solar sends out. If there's a deficiency, the house is pulling a heavy load, clouds are blocking the panels, etc., it will turn up the inverter output.

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Nevetsyad: thank you for the explanation. So, if I understand correctly, in case of a power outage (and usual caveats about the sun shinning), the powerwall2 will be able to supply power to, let's say, critical loads (appropriately wired, of course) AND recharge itself as long as the panels are producing power. Am I right?

Details - start with the big picture. This thread is about PowerWall 2.0 + Enphase. You are asking about off-grid.
- Do you want to take your Enphase solar off-grid?
- Will you add new solar directly connected to the PowerWall inter-operating with the existing Enphase solar?
- How many watts of solar for each?
- At your location, what is your min and max generation across seasons for your existing solar?
- What is your peak draw from household loads?
- How many PowerWall units do you think you need?
- What is your kWh usage across seasons?
- Have you modeled your energy shortfall in the Winter? This would include looking through your history for consecutive low generation days.
- How did you reach the conclusion that you only need 1kW backup supply?

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Answered in order ...

Big picture: I want my home to run an integrated PV/battery/plug-in that is no more expensive than my current 100% fossil based system. The battery will replace my current tie-in to the grid and save my $30 a month connection charges (and the pernicious bureaucracy of the utility that makes PV expensive to install.) I am not trying to reach zero carbon, only reduce fossil fuel use as much as possible. Domestic hot water and home heating is NG based so the PV system is only expected to cut my fossil fuel use for personal transport and electricity. This is a good start because 100% of my electricity is currently coal sourced and if my estimates are correct I will reduce my personal transport petrol use to about 100 gallons a year.

-Yes. I have not built the PV yet, so I have choices in system design. E.g. could the PW 2.0 save me an inverter ? I tried calling SolarEdge but they were not conversant with PW 2.0. I do want to use micro-inverters because I have variable shading through the day. I have a call in to Tesla to clarify what circumstances a PW 2.0 will be able to take generator input (in this case a Toyota hybrid that can output close to 1 kW from the 12v as DC.

See (1)

Total Max PV DC solar will be ~ 3 kW. This is an over-build for my expected use to cover some of the winter days with low solar.

PVWatts gives monthly estimates. Per 3 kW, about 15 kWh a day in the winter and 22 kWh a day in the summer for the fixed array I have chosen

Under 1 kW for the home, and up to another 3.8 kW for a plug-in Prius. When the M3 arrives I'll add another PW if needed for either peak load or TOU. My seasonal kWh use does not vary much --- about 4 kWh a day in the summer, spring and fall and 6 kWh a day in the winter. This does not include car use which is 10-20 miles every day and 90 miles twice a week. If there is not enough sun I will run the car on petrol. I estimate 4 miles per kWh for our driving habits based on extensive record keeping for our current Prius cars. The first plug-in will be a Prius Prime.

For now, One .... IF I can recharge the PW from the plug-in to cover those periods of no sunshine for > 48 hours straight.

See (5)

I don't have accurate data for how many episodes of greater than 48 hours without sunshine. Not many. Ten ? Twenty seems a pessimistic outlier. This is why ability to charge the PW 2.0 with the car as a generator is important.

One kW will let me charge up the PW 2.0 in about 8 hours. I am home every day for 12 hours (I work at night), and for now either of two cars can be a generator. When the M3 arrives there will always be one car that can be the generator.

Big picture: I want my home to run an integrated PV/battery/plug-in that is no more expensive than my current 100% fossil based system. The battery will replace my current tie-in to the grid and save my $30 a month connection charges (and the pernicious bureaucracy of the utility that makes PV expensive to install.) I am not trying to reach zero carbon, only reduce fossil fuel use as much as possible. Domestic hot water and home heating is NG based so the PV system is only expected to cut my fossil fuel use for personal transport and electricity. This is a good start because 100% of my electricity is currently coal sourced and if my estimates are correct I will reduce my personal transport petrol use to about 100 gallons a year.

-Yes. I have not built the PV yet, so I have choices in system design. E.g. could the PW 2.0 save me an inverter ? I tried calling SolarEdge but they were not conversant with PW 2.0. I do want to use micro-inverters because I have variable shading through the day. I have a call in to Tesla to clarify what circumstances a PW 2.0 will be able to take generator input (in this case a Toyota hybrid that can output close to 1 kW from the 12v as DC.

See (1)

Total Max PV DC solar will be ~ 3 kW. This is an over-build for my expected use to cover some of the winter days with low solar.

PVWatts gives monthly estimates. Per 3 kW, about 15 kWh a day in the winter and 22 kWh a day in the summer for the fixed array I have chosen

Under 1 kW for the home, and up to another 3.8 kW for a plug-in Prius. When the M3 arrives I'll add another PW if needed for either peak load or TOU. My seasonal kWh use does not vary much --- about 4 kWh a day in the summer, spring and fall and 6 kWh a day in the winter. This does not include car use which is 10-20 miles every day and 90 miles twice a week. If there is not enough sun I will run the car on petrol. I estimate 4 miles per kWh for our driving habits based on extensive record keeping for our current Prius cars. The first plug-in will be a Prius Prime.

For now, One .... IF I can recharge the PW from the plug-in to cover those periods of no sunshine for > 48 hours straight.

See (5)

I don't have accurate data for how many episodes of greater than 48 hours without sunshine. Not many. Ten ? Twenty seems a pessimistic outlier. This is why ability to charge the PW 2.0 with the car as a generator is important.

One kW will let me charge up the PW 2.0 in about 8 hours. I am home every day for 12 hours (I work at night), and for now either of two cars can be a generator. When the M3 arrives there will always be one car that can be the generator.

Thanks for your interest and help!

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A. I assume that the PowerWall 2.0 has an internal inverter and has a HVDC input for one or more solar strings. I also assume that they will support some kind of DC optimizers, so there would be no advantage to using Enphase inverters at all. In fact, it would likely be a cost penalty and add another layer of integration complication. The generator input is the biggest open question.
B. If your usage figures are correct, a single PowerWall and the solar you have specified should keep you down to a handful of days that you would need to fill in with the "generator". You would definitely need some kind of alert or notification system when the PowerWall reaches some low setpoint where you would want to go connect and turn on the generator. In this case, you would have to turn on the car, turn on the 12V inverter and run the 120V power cord to the generator input.
C. If you want to charge the Prius Prime from this system, you probably want to get an EVSE that can vary the pilot signal or just use one that is always low power, like 240V 12A. EVSEupgrade or OpenEVSE is a good fit for this. You will have to pay attention to weather forecast and the SOC of the PowerWall to decide if you're going to charge the car. Maybe there could be some way automate this so you just plug in the car and the system decides when and how much to charge the car. There will be a lot more days that you won't have surplus energy to charge the car than the days where the house alone falls short and you need to add energy from the generator.
D. When you get the Model 3 you will have to seriously think about how many miles per day you want to recharge from this system and where you will charge it when you are short on energy at home. Of course, you can add more solar and another PowerWall, but that still won't be able to recharge a Model 3 from flat empty when you return from a trip. If you had 2 PowerWalls and 10kW of solar, you would probably never have to connect the generator, but there would be many winter days that you would have to charge the Model 3 elsewhere.

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